Sound-absorbing material for automobile using foaming urethane foam to which carbon nano-tube is applied and preparation method thereof

ABSTRACT

Disclosed is a sound-absorbing material for an automobile, using foaming urethane foam to which carbon nano-tubes are applied, and a preparation method thereof. More particularly, disclosed is a sound-absorbing material for an automobile, which has excellent sound absorption and insulation performance while maintaining excellent flame retardancy, by increasing the ratio of open cells while uniformly maintaining the cell structure of the foam by adding carbon nano-tubes as a substitute for a portion of a flame retardant filler, and a preparation method thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of Korean Patent Application No. 10-2013-0030450 filed in the Korean Intellectual Property Office on Mar. 21, 2013, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a sound-absorbing material for an automobile including a foaming urethane foam to which a carbon nano-tube is applied, and a preparation method thereof. More particularly, the present invention relates to a sound-absorbing material for an automobile, which has excellent sound absorption and insulation performance even while maintaining excellent flame retardancy. In particular, the sound-absorbing material is provided with an increased ratio of open cells while uniformly maintaining a cell structure of the foam by adding a carbon nano-tube as a portion of a flame retardant filler to a semi-rigid foaming urethane foam

BACKGROUND ART

In an automobile, noise is continuously generated in an engine during its operation, and the noise generated enters the automobile interior compartment through a body dash panel, or it is discharged to the outside of the automobile through the car body chassis. Various sound absorption and insulation parts are mounted in the vehicle in order to reduce the engine noise, and representative examples thereof include a hood insulator, a dash insulator, and the like.

Traditionally, resinated felt, glass wool, and the like have been used as materials for an engine room absorption and insulation part. However, these materials are disadvantageous in that a large weight is required in order to adequately improve sound-absorption and sound-insulation performance. Further, these materials are disadvantageous in that hazardous materials, such as odor and the like, of non-dispersible resins in the materials are emitted after aging.

Studies have been conducted on potential replacement materials in order to solve these problems. Foaming polyurethane foam has been considered, but it emits hazardous materials similar to the existing materials. However, polyurethane foam is advantageous in that hardness and physical properties may be easily adjusted by adjusting the blending thereof. Further, foaming polyurethane foam has better sound-absorbing performance and is lighter in weight than existing resinated felt and glass. As such, it is expected to reduce automobile noise and improve fuel efficiency.

However, while semi-rigid foaming polyurethane foam exhibits better performance than the existing materials in mid and low frequency regions of 1,500 Hz or less, its performance is relatively insufficient in a high frequency region.

In order to compensate for these drawbacks, Korean Patent Application Laid-Open No. 10-2011-107675 suggests a technology in which polyurethane foam is formed by adding and dispersing carbon nano-tubes or carbon nano-tubes and carbon nano-plates to a polyurethane undiluted solution to produce foam that when used as an insulation material, improves durability, insulation property, and thermal stability. However, while improved performance may be expected by this technology, there is a problem in that sound-absorbing performance is very weak because rigid foam is applied rather than semi-rigid foaming products. Rigid foaming urethane foam is an independently closed cell structure and has a form in which heat insulation and cold keeping characteristics are reinforced by confining gas therein. Such foam is generally used as a product for construction. In addition, once rigid polyurethane foam is foamed, it may not be thermally molded into another shape, which is required for press molding into a part shape. Therefore, rigid polyurethane foam is not suitable for use as a sound absorption and insulation material for an automobile.

The reason why rigid foaming polyurethane foam has a closed cell structure as described above is that an internal cell structure forms a mesh-type network due to the structure of the main undiluted solution and the composition of other additives. Furthermore, in order for rigid foaming polyurethane foam to be used as a sound-absorbing material for an automobile engine room, the rigid foaming polyurethane foam needs to have flame retardancy, that is, a self-extinguishing property that naturally extinguishes fire within a predetermined time even when fire is ignited. Thus, it is difficult to solve the problem by mixing carbon nano-tube alone.

Further, technologies which use a carbon nano-tube include Korean Patent Application Laid-Open No. 10-2008-3843, which proposes a polymerizing cell structure including carbon nano-tubes, in which the cell has an average size less than 150 μm, and carbon nano-tube is included in an amount less than 60% by weight, preferably from 10% by weight to 50% by weight or preferably from 0.1% by weight to 3% by weight based on the total weight of the polymer structure. Japanese Patent Application Laid-Open No. 2008-13802 proposes a polyurethane foaming body for a vehicle, which contains expanded graphite and which is used to remove noise entering a partition wall of an engine room. Japanese Patent No. 3,580,011 proposes a paint form for forming a coating film by a sound-proofing treatment method of an automobile engine, wherein the paint contains an acrylic resin emulsion, a body pigment, and a flake filler such as graphite and the like. Korean Patent Application Laid-Open No. 10-2011-107838 proposes a technology in which carbon nano-tubes and the like are used in a viscoelastic core used as a structural composite with improved sound-proofing and dust resistant characteristics, and which is applied to an exterior plate of an airplane fuselage, and the like.

However, these technologies have different resin components in which the carbon nano-tubes are provided, and most of these resin components are composed of rigid foaming bodies. Thus, there is a problem in that physical properties suitable for providing a lightweight material for implementation in an automobile are insufficient, and the sound-absorbing performance is generally insufficient.

SUMMARY OF THE INVENTION

The present invention provides a material in which nano-sized fine particle carbon nano-tubes are added to semi-rigid polyurethane foam along with a flame retardant filler in order to improve mid and high frequency performances, wherein sound-absorbing performance is outstandingly improved even in mid and high frequency regions of about 1,500 Hz or more.

According to one aspect, the present invention provides a sound-absorbing material for an automobile including foaming urethane foam to which carbon nano-tubes are applied. The sounds-absorbing material of the present invention improves fuel efficiency due to its lightweight nature, improves sound absorption and insulation performance over the entire frequency band, and has excellent flame retardancy.

According to another aspect, the present invention provides a method of preparing a sound-absorbing material for an automobile which uses foaming urethane foam to which carbon nano-tubes are applied, wherein the material is capable of being subjected to thermal press molding into a desired form of a part for an automobile, and wherein the material simultaneously satisfies the required high sound-absorbing and flame retardant properties.

An exemplary embodiment of the present invention provides a sound-absorbing material for an automobile, using foaming urethane foam to which carbon nano-tube is applied, including: a polypropylene-based polyol component and an isocyanate component as main components. In particular, the sound-absorbing material is formed of a foaming undiluted solution including 100 parts by weight of a polyol component, about 120 to 180 parts by weight of isocyanate, about 10 to 20 parts by weight of a flame retardant filler, and about 0.1 to 3 parts by weight of carbon nano-tube, wherein parts by weight are based on 100 parts by weight of the polyol component. In particular, the polyol component includes about 70 to 90% by weight of high-molecular and low-molecular polyols and about 10 to 30% by weight of at least one additive including a foaming agent, wherein wt % are based on total weight of the polyol component. Preferably, the polyol component consists of about 70 to 90% by weight of high-molecular and low-molecular polyols and about 10 to 30% by weight of at least one additive. According to various embodiments, the sound-absorbing material includes a sliced foaming polyurethane foam, particularly having the above-described components.

According to various embodiments, a non-woven fabric may be additionally press-molded on both surfaces of the sound-absorbing material for an automobile.

Another exemplary embodiment of the present invention provides a method of preparing a sound-absorbing material for an automobile, using foaming urethane foam to which carbon nano-tube is applied, the method including: mixing about 70 to 90% by weight of high-molecular and low-molecular polyols with about 10 to 30% by weight of an additive including a foaming agent to prepare 100 parts by weight of a polyol component; adding a mixed raw material to the polyol component and using a stirrer or the like for foaming thereinto and mixing the resulting mixture by stirring to prepare a foaming undiluted solution, wherein the raw material is prepared by mixing about 120 to 180 parts by weight of isocyanate, about 10 to 20 parts by weight of a flame retardant filler, and about 0.1 to 3 parts by weight of carbon nano-tube, based on 100 parts by weight of the polyol component; injecting the foaming undiluted solution into a mold to age the solution into a polyurethane foam which is foamed; and slicing the foaming polyurethane foam.

In addition, the method may further include: additionally adhering a non-woven fabric on both surfaces of the sound-absorbing material for an automobile as prepared above; press-molding the laminate in a thermal molding machine, and then press-cooling the laminate in a cooling jig to prepare a semi-product; and trimming the semi-product into a desired design shape.

The sound-absorbing material for an automobile, including foaming urethane foam to which carbon nano-tubes are applied may use a composite polyurethane foam to which the carbon nano-tubes are applied, and which may be thermally molded into an engine room part such as a dash outer, a hood insulator, a dash insulator, and the like for an automobile engine room. Such a material satisfies applicable flame retardancy requirements for use in an automobile.

The sound-absorbing material for an automobile according to the present invention may further provide improved Noise, Vibration, and Harshness (NVH) over the entire frequency region compared to conventional materials, and enhances the quality and fuel efficiency of an automobile by being a light weight and environmentally friendly material.

Furthermore, the present invention makes it possible to achieve flame retardancy and a self-extinguishing property by mixing carbon nano-tubes with graphite and using the mixture in a polyurethane foam. Such properties have not been achieved to date by exiting technologies which add carbon nano-tubes to a polyurethane foam.

In addition, the present invention makes it possible to secure excellent physical properties of molding a hot rolled part which has not been possible with conventional polyurethane foams to which carbon nano-tubes are added.

Other aspects and exemplary embodiments of the invention are discussed infra.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:

FIG. 1 is a graph showing results of sample sound-absorbing performance experiments as performed in Example 2 and Comparative Examples 1 to 3 according to an embodiment of the present invention.

FIG. 2 is a graph comparing sound-absorbing performances in Examples 1 to 3 according to embodiments of the present invention.

FIG. 3 is a graph comparing sound insulation characteristics of Example 2 and Comparative Example 3 according to an embodiment of the present invention through an actual vehicle transmission sound test.

FIG. 4 is a photograph of a cell structure of the polyurethane foam according to an embodiment of the present invention by scanning electron microscopy.

It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

Hereinafter, the present invention will be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

The unrelated parts to the description of the exemplary embodiments are not shown to make the description clear and like reference numerals designate like element throughout the specification.

Further, the sizes and thicknesses of the configurations shown in the drawings are provided selectively for the convenience of description, so that the present invention is not limited to those shown in the drawings and the thicknesses are exaggerated to make some parts and regions clear.

Throughout the specification, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.

Further, the terms, “ . . . unit”, “ . . . mechanism”, “ . . . portion”, “ . . . member” etc. used herein mean the unit of inclusive components performing at least one or more functions or operations.

It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g., fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about”.

Hereinafter, an exemplary embodiment of the present invention will be described in detail as follows.

The present invention provides a sound-absorbing material for an automobile which consists of a polyurethane foam including a polypropylene-based polyol component and an isocyanate component as main components. The present material has excellent physical properties by substituting a portion of a flame retardant filler added to the polyurethane foam with carbon nano-tubes.

In the present invention, the polyol component of the sound-absorbing material for an automobile, includes, and preferably consists of, about 70 to 90% by weight of high-molecular and low-molecular polyols and about 10 to 30% by weight of one or more additives including a foaming agent, wherein wt % are relative to the total weight of the polyol component. As the high-molecular polyol used herein, a polyol having a weight average molecular weight in a range from about 3,000 g/mol to about 6,000 g/mol may be used, and as the low-molecular weight, a polyol having a weight average molecular weight in a range of about 1,500 g/mol or less (but greater than 0) may be used, for example about 1,000 g/mol to about 1,500 g/mol. As the polyol, a polypropylene-based polyol is preferably used, and more preferably, polypropylene glycol (PPG) is used. The polyol component contains an additive in which a foaming agent is included in the high-molecular and low-molecular polyol, and, for example, it is preferred that one or more selected from a cell opener, a chain-extender, a flame-retardant, a surfactant, and a catalyst are mixed as the additive along with the foaming agent. Here, in the polyol component, a high-molecular polypropylene-based polyol and a low-molecular polypropylene-based polyol are preferably used in amounts from about 40% by weight to about 60% by weight and from about 20% by weight to about 40% by weight, respectively, wherein wt % is based on total weight of the polyol component. In connection with the additives mixed therewith, it is preferred that water is used as the foaming agent in an amount from about 5% by weight to about 10% by weight. With respect to the cell opener, for example, a polyether-based foam opener may be used in an amount from about 1% by weight to about 5% by weight. As the chain-extender, for example, a functional material such as ethylene glycol, butanediol, triethanol amine, glycerin, and the like may be used in an amount from about 2% by weight to about 6% by weight. With respect to the flame-retardant, a phosphorus-based flame-retardant may be used in an amount from about 3% by weight to about 10% by weight. As the surfactant, for example, a silicone surfactant may be used in an amount from about 1% by weight to about 3% by weight. With respect to the catalyst, for example, an amine catalyst may be used in an amount from about 0.1% by weight to about 3% by weight. The aformentioned wt % are relative to the total weigh of the polyol component The additives including the foaming agent may be added in an amount from about 10 parts by weight to about 30 parts by weight, relative to 100 parts by weight of the polyol component. AS referred to herein, a component with which an additive including a foaming agent has been mixed in addition to the pure high-molecular and low-molecular polyols as described above is referred to as the polyol component for convenience.

The polyol component of the present invention may be controlled so as to have different characteristics of a polyurethane material in the soft, semi-rigid, and rigid form by controlling the above-described constitution thereof. In particular, when the polyol component is constituted with the above-described composition, it is possible to prepare a semi-rigid foaming polyurethane foam, which is the most suitable for the object of the present invention, in combination with other components to be described below.

According to an embodiment of the present invention, isocyanate, a flame retardant filler, and carbon nano-tubes are added to and mixed with the polyol component. In particular, a polyurethane foam is provided which is formed of a foaming undiluted solution including about 120 parts by weight to about 180 parts by weight of isocyanate and more preferably about 150 parts by weight to about 160 parts by weight of isocyanate, about 10 parts by weight to about 20 parts by weight of the flame retardant filler and even more preferably about 14 parts by weight to about 16 parts by weight of the flame-retardant filler, and about 0.1 part by weight to about 5 parts by weight of carbon nano-tubes, based on 100 parts by weight of the polyol component. In the present invention, essentially, it may be said that the flame retardant filler has been partially substituted with the carbon nano-tubes. In particular, it is preferred that about 1% by weight to about 20% by weight of the flame retardant filler is substituted with carbon nano-tubes. The flame retardant filler is substituted with carbon nano-tube in order to adjust the formation of a cell structure which is associated with improvement of sound-absorbing performance of the polyurethane foam.

In the present invention, the isocyanate may be any conventional isocyanate and, preferably, is a modified methylene diphenyl diisocyanate (MDI) having an NCO content from about 30% by weight to about 35% by weight. Furthermore, any conventional flame retardant fillers may be used, with graphite being one preferred example of a suitable flame retardant filler.

The carbon nano-tube used in the present invention may be any conventional carbon nano-tube. Preferably, the carbon nano-tube has a single-wall or multi-wall structure having a diameter from about 10 nm to about 50 nm, a volume density from about 0.02 g/Ml to about 1.5 g/Ml, a purity from about 85% to about 90%, and a degree of crystallinity (I_(Γ)/I_(Δ)) from about 0.7 to about 1.1. The carbon nan-tube may be included in the composition in the form of a powder, a powdered granule, and the like.

Graphite and carbon nano-tubes, which are preferably used as the flame retardant fillers, secure flame retardancy of the polyurethane foam as the same carbon component material. However, the carbon nano-tube is a material having a very light specific gravity. As such, when the carbon nano-tubes are added in an extremely large amount in the process, the volume is too big compared to the mass thereof. Thus, the use of carbon nano-tubes is not preferable in the actual process and leads to deterioration in physical properties. Further, when carbon nano-tubes are excessively introduced into the composition, the viscosity of the undiluted solution constituting the polyurethane foam is increased to a considerably high level. This makes it difficult to mix the carbon nano-tubes with other additive components, which makes the foam state thereof very poor. Therefore, the use of carbon nano-tubes in the present invention and the amount added have very important technical significance and critical significance. As such, it is preferred that carbon nano-tubes are added in the above-described range. It is more preferred that carbon nano-tubes are added in an amount of approximately about 0.1% by weight to about 1.1% by weight based on the total amount of the foaming undiluted solution.

The sound-absorbing material for an automobile according to the present invention is formed of a foaming undiluted solution including the above-described components. According to various embodiments, the sound-absorbing material is in the form of a sliced foaming polyurethane foam.

According to various embodiments, the sound-absorbing may basically be formed of a semi-rigid foaming polyurethane foam having a density from about 18 k/m³ to about 20 k/m³.

The sound-absorbing material for an automobile according to the present invention contains carbon nano-tubes (CNT) in the polyurethane foam in an amount from about 0.1% by weight to about 3.0% by weight based on the total weight of the polyol component, and from about 0.1% by weight to about 1.1% by weight based on the entire semi-rigid foaming polyurethane mixture undiluted solution. The thus formed material exhibits a maximized sound-absorbing performance over the entire frequency region, particularly due to an enhancement of gas permeability and an improvement of physical properties resulting from a change in the ratio of open cells in the foaming polyurethane foam cell structure and a change in hardness.

As described above, according to an exemplary embodiment of the present invention, the ratio of open cells is increased while the cell structure of the foam is uniformly maintained by adding carbon nano-tube fine particles to a foaming polyurethane foam material. In addition, the hardness of the semi-rigid polyurethane foam is alleviated. Through this, the NVH performance is outstandingly improved over the entire frequency region. However, it has been found that as the content of carbon nano-tube (CNT) is increased, the ratio of open cells is not absolutely increased. In particular, when carbon nano-tubes are contained in an excessive amount, the viscosity is increased due to the addition of nano-size fine particles, and thus the ratio of open cells may be conversely decreased. Therefore, by suitably controlling only the component composition of the foaming undiluted solution constituting the semi-rigid foaming polyurethane foam and the content of a carbon nano-tube (CNT) additive so as to provide the physical properties required for a product in an appropriate range in accordance with the present invention, the cell structure thereof may be optimized. As described above, it is important to form the sound-absorbing material with the described constitution so as to further improve the NVH performance of an automobile.

The application of carbon nano-tubes (CNT) to improve the sound-absorbing performance of foaming polyurethane foam according to the present invention is different from the technology to which a general carbon nano-tube known in the related art is applied. The foaming undiluted solution according to the present invention has a different series of compositions, and thus only in the present invention is it possible to achieve the properties required for an excellent sound-absorbing material.

The characteristics of the sound-absorbing material for an automobile according to the present invention may be confirmed through a cell structure having the biggest impact on the performance of the sound-absorbing material. It was confirmed through scanning electron microscopy that the cell structure of the present material became homogenized and that a change in the ratio of open cells occurred by applying carbon nano-tubes having the constitution of the present invention. Further, a flow resistivity measurement was carried out in order to substantially confirm the change in the open cell ratio. The measurements demonstrated that the foaming urethane foam to which carbon nano-tubes were applied according to the present invention exhibited a lower resistance value as compared to a foam to which the constitution of the present invention was applied, which demonstrated that gas permeability was improved in the material of the present invention. In particular, the present invention outstandingly improved the sound-absorbing performance due to homogenization of the cells and an increase in the gas permeability effect.

Furthermore, in order to confirm the effect of the sound-absorbing material of the present invention, the sound-absorbing performances were compared and tested based on an original material sample of the main sound-absorbing materials for the engine room. As a result, it was confirmed that the sound-absorbing material consisting of a foaming polyurethane foam to which carbon nano-tubes (CNT) were applied according to the present invention exhibited the best performance as compared to the conventional sound-absorbing material and a sound-absorbing material having a constitution different than that of the present invention. In these tests, the sound-absorbing performance was measured using a small reverberation chamber manufactured by German Rieter Technologies AG.

Meanwhile, in the present invention, a non-woven fabric many be additionally press-molded on both surfaces of the above-described sound-absorbing material for an automobile.

An exemplary embodiment of the method of preparing the sound-absorbing material for an automobile, using foaming urethane foam to which carbon nano-tube is applied according to the present invention as described above will be described as follows.

Typically, in order to prepare the sound-absorbing material for an automobile according to the present invention, 100 parts by weight of a polyol component is prepared by mixing about 70% by weight to about 90% by weight of high-molecular and low-molecular polyols with about 10% by weight to about 30% by weight of at least one additive including a foaming agent, wherein wt % are based on the total weight of the polyol component.

Separately from this, a mixed raw material is prepared by mixing about 140 parts by weight to about 170 parts by weight of isocyanate, about 13 parts by weight to about 18 parts by weight of a flame-retardant, and about 0.1 part by weight to 3 about parts by weight of carbon nano-tubes particularly by using a stirrer or the like for foaming, wherein parts by weight are relative to 100 parts by weight of the polyol component. At this time, it is suitable to perform mixing using the stirrer or the like for foaming for about 20 to 60 seconds, and more preferably for about 25 to 35 seconds.

A foaming undiluted solution is then prepared by introducing the prepared mixed raw material into the polyol component and mixing the mixture under stirring. At this time, the mixing under stirring is preferably performed preferably at a high speed from about 1,000 rpm to about 2,000 rpm for about 5 to about 20 seconds, and more preferably at such a high speed for about 8 to about 12 seconds.

The foaming undiluted solution is then injected into a mold and aged as a polyurethane foam which is foamed. At this time, the polyurethane foam is preferably aged for about 2 days to about 5 days, and most preferably for approximately 3 days.

A sound-absorbing material for an automobile, using the foaming urethane foam, to which carbon nano-tubes are applied, is then preferably prepared by thinly slicing the polyurethane foam into a predetermined thickness.

According to various embodiments, the method of preparing a sound-absorbing material for an automobile according to the present invention further include: additionally adhering a non-woven fabric on both surfaces (top and bottom surfaces) of the sound-absorbing material for an automobile (e.g. after the polyurethane foam is thinly sliced) to provide a laminate; press-molding the laminate in a thermal molding machine, and then press-cooling the laminate in a cooling jig to prepare a semi-product; and trimming the semi-product into a desired design shape.

Here, when a non-woven fabric is adhered on both surfaces of the sound-absorbing material, the laminate is preferably press-molded in a thermal molding machine at a predetermined temperature, preferably from about 170° C. to about 190° C. preferably for about 30 seconds to about 60 seconds to thereby attach the non-woven fabric thereto. Then, preferably immediately after the molding, a semi-product is produced by press-cooling the laminate in a cooling jig again for about 30 seconds to about 60 seconds to control the shrinkage of the non-woven fabric and the sound-absorbing material. Thereafter, and a sound-absorbing material having a finished product form, which is appropriate for a specifically applied site, may be completed by trimming the semi-product into a desired design shape.

As described above, a product made of the sound-absorbing material for an automobile using foaming polyurethane foam to which carbon nano-tubes are added according to the present invention may be prepared by selectively using a general non-woven fabric or a reinforced/water repellent non-woven fabric, if desired, in order to change the strength of the product suitably for physical properties required by each automobile manufacturer.

According to the present invention, the sound-absorbing material was used to manufacture a dash outer (the dash outer being a component used in an engine compartment acoustic part) of an actual vehicle, and then transmission loss (TL) was measured. Based on the results, an improvement in a range from about 500 Hz to about 2,500 Hz by about 0.3 dB was exhibited. In the case of the outer dashboard, the ratio of the area occupied by the outer dashboard in an NVH product applied to the entire vehicle is not large, and thus improvement in transmission noise is significant.

Significantly, the present invention provides a technology in which sound-absorbing performance is improved by adding carbon nano-tubes to a material, and wherein flame retardancy and self-extinguishing property may be further secured by adding graphite thereto. The present invention further provides a technology in which the sound-absorbing material may be applied to a part for an actual automobile engine room.

In general, a product manufactured of a sound-absorbing material made of a polyurethane foam material has a low strength compared to the existing sound-absorbing material, and thus it is necessary to compensate for the low strength. Therefore, in order to improve this drawback, the present invention laminates a high rigidity water repellent non-woven fabric on both surfaces of urethane foam, followed by thermal molding, if necessary. The high rigidity water repellent non-woven fabric may be used by increasing the amount of a low-melting point fiber used in order to serve as an adhesive while maintaining moldability compared to the existing general non-woven fabric. Further, in order to compensate for the rigidity and resistance to moisture, a water repellent may be added to the surface thereof, and thus the high rigidity non-woven fabric may be selectively provided based on the desired use environment. However, the non-woven fabric which may be used in the present invention is not limited to the high rigidity water repellent non-woven fabric. For example, a product of the present invention may be completed by laminating a general non-woven fabric or a high rigidity water repellent non-woven fabric on both surfaces of the material, and then subjecting the laminate to a thermal molding press molding machine.

Therefore, the present invention provides a sound-absorbing material for an automobile which is made of composite polyurethane foam to which carbon nano-tubes are added, wherein the material is capable of being thermally press molded into a part shape for application to any part of an automobile. The material of the present invention achieves a high sound-absorbing property required for use as the sound-absorbing material for an automobile and simultaneously satisfies flame retardancy requirements.

Hereinafter, the present invention will be described in detail with reference to the following Examples, but it is not limited by the Examples.

Examples 1 to 3

A foaming polyurethane foam was prepared according to the composition ratio shown in the following Table 1 (wherein the units are parts by weight). A high-molecular polyol and each additive (cell opener, chain-extender, flame-retardant, catalyst, and water) were mixed with each other in the foaming polyurethane foam, and a mixed raw material in which a low-molecular polyol, and graphite and carbon nano-tube as flame retardant fillers had been mixed were mixed with each other by a foaming machine, thereby preparing a foaming undiluted solution. At this time, carbon nano-tubes were added in an amount of 0.1% by weight (Example 1), 0.3% by weight (Example 2), and 0.5% by weight (Example 3), respectively, for the polyol components in the following Table 1. The foaming undiluted solution was added to a mold so as to form a polyurethane foam, and the polyurethane foam was subjected to aging for 3 days, and then sliced into a thickness of 1.5 mm.

A chemical-based reinforced water repellent non-woven fabric impregnated with silicone resin was attached to both surfaces of the sliced polyurethane foam, and the laminate was press-cooled by a metal die cooling jig in a thermal molding machine at 180° C. to prevent shrinkage due to bonding the non-woven fabric and the polyurethane foam material, thereby manufacturing a first semi-product. A sound-absorbing material for an engine room NVH part was prepared by trimming the semi-product thus formed into a final product design shape.

Examples 4 to 6

A sound-absorbing material was prepared in the same manner as in Example 1, except that carbon nano-tubes were added thereto according to the compositions in the following Table 1.

Comparative Examples 1 and 2

When a non-woven fabric and resinated felt 1200 were used, a sound-absorbing material was constituted by using 450 g of glass wool between the non-woven fabrics. In particular, the resinated felt 1200 and/or glasswool 450 is applied in between the non-woven fabrics.

Comparative Example 3

A sound-absorbing material was constituted in the same manner as in Example 2, except that a polyurethane foam was prepared without adding carbon nano-tubes and the polyurethane foam was used as such.

TABLE 1 Comparative Examples 4, 5, Classification Example 3 and 6 Remarks Polyol POLYOL A 48 48 High-molecular component PPG (PPG) POLYOL B 29 29 Low-molecular PPG Cell opener 3 3 Cell opener polyol Chain-extender 4 4 Flame- 6 6 retardant Surfactant 1.5 1.5 Catalyst 1 1 AMINE Water 7.5 7.5 Foaming agent Total 100 100 — Isocyanate MODIFIED MDI 155 155 NCO: 32.1% (ISO) Flame GRAPHITE 15 14.85 14.25 13.65 Flame retardant retardancy filler Cabon Nano- — 0.15 0.75 1.35 Carbon Nano- Tube Tube

Experimental Example 1

Physical properties of the sound-absorbing materials according to Examples 1 to 3 and Comparative Example 3 were measured, and are shown in the following Table 2.

TABLE 2 Comparative Classification Unit Example 3 Examples 1, 2, and 3 Density kg/m³ 17.83 18.33 18.36 18.25 Tensile strength kfg/cm² 0.91 0.82 0.79 0.80 Flexural strength kfg/cm² 0.38 0.62 0.60 0.56 Elongation % 13.94 13.71 13.20 12.87 Compressive strength kfg/cm² 0.28 0.27 0.28 0.26 Flow resistivity MKS Havl 539,518 507,921 321,599 294,452 NVH performance — ◯ ◯ ⊚ ⊚

In Table 2, ◯ and ⊚ denote excellent and very excellent levels in the NVH performance, respectively.

Experimental Example 2

Physical properties of the sound-absorbing materials according to Example 2 and Comparative Examples 1 to 3 were measured, and are shown in the following Table 3. Here, A, B, C, and D denote very excellent, excellent, good, and poor, respectively.

TABLE 3 Comparative Comparative Comparative Classification Example 1 Example 2 Example 3 Example 2 Weight A B B A NVH D C B A performance Cost C C B B

Experimental Example 3

As a result of testing the sample sound-absorbing performances of Example 2 and Comparative Examples 1 to 3, as shown in the graph in FIG. 1, Example 2 exhibited the best result.

Experimental Example 4

As a result of comparing the sound-absorbing performances of Examples 1 to 3, as shown in the graph in FIG. 2, all of the Examples exhibited excellent sound-absorbing performances.

Experimental Example 5

As a result of comparing sound insulation characteristics through an actual vehicle transmission noise test of Example 2 and Comparative Example 3, as shown in the graph in FIG. 3, Example 2 (line represented by −6) exhibited excellent sound insulation performance even at 2,500 Hz or more.

As a result of these experiments, the principle that the sound-absorbing performance of foaming polyurethane foam is improved by applying carbon nano-tube (CNT) so as to provide a cell structure having the greatest impact on performance was confirmed. That is, from the experimental results, it was confirmed by scanning electron microscopy that the cell structure had been homogenized and that the ratio or open cells was changed by applying carbon nano-tube according to the present invention (see photograph of FIG. 4), and as a result of using a flow resistivity measurement for substantial measurement of the change in open cell ratio, a foaming urethane foam to which carbon nano-tubes were applied exhibited a low resistance value compared to a foam without carbon nano-tubes, which means that gas permeability was improved. That is, the sound-absorbing performance was outstandingly improved due to homogenization of the cells and an increase in gas permeation effect provided by the present invention. For the main sound-absorbing material for the engine room, the sound-absorbing performances in the Comparative Examples were compared and tested through the existing material sample. As a result, it was confirmed that the foaming polyurethane foam to which carbon nano-tubes (CNT) were added according to the present invention had the best performance (see FIG. 1). The sound-absorbing performance was measured using a small reverberation chamber manufactured by German Rieter Technologies AG.

While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 

What is claimed is:
 1. A sound-absorbing material for an automobile, using foaming urethane foam to which carbon nano-tubes are applied, comprising: 100 parts by weight of a polypropylene-based polyol component, the polyol component comprising about 70 to 90% by weight of high-molecular and low-molecular polyols and about 10 to 30% by weight of at least one additive comprising a foaming agent, wherein wt % are based on the total weight of the polyol component; and an isocyanate component, comprising about 120 to 180 parts by weight of isocyanate, about 10 to 20 parts by weight of a flame retardant filler, and about 0.1 to 3 parts by weight of carbon nano-tubes, wherein parts by weight are based on 100 parts by weight of the polyol component.
 2. The sound-absorbing material for an automobile of claim 1, wherein the at least one additive comprises about 5% by weight to about 10% by weight of water as the foaming agent, about 1% by weight to about 5% by weight of a cell opener, about 2% by weight to about 6% by weight of a chain-extender, about 3% by weight to about 10% by weight of a phosphorus-based flame-retardant, about 1% by weight to about 3% by weight of a silicone surfactant, and about 0.1% by weight to about 3% by weight of an amine catalyst, wherein wt % are based on the total weight of the polyol component.
 3. The sound-absorbing material for an automobile of claim 1, wherein the carbon nano-tubes are present in an amount from about 1% by weight to about 20% by weight based on the weight of the flame retardant filler.
 4. The sound-absorbing material for an automobile of claim 1, wherein the isocyanate is a modified methylene diphenyl diisocyanate (MDI) having an NCO content from about 30% by weight to about 35% by weight.
 5. The sound-absorbing material for an automobile of claim 1, wherein the carbon nano-tubes have a single-wall or multi-wall structure having a diameter from about 10 nm to about 50 nm, a volume density from about 0.02 g/Ml to about 1.5 g/Ml, a purity from about 85% to about 90%, and a degree of crystallinity (I_(Γ)/I_(Δ)) from about 0.7 to about 1.1.
 6. The sound-absorbing material for an automobile of claim 1, wherein the carbon nano-tubes are in the form of a powder or a powdered granule.
 7. The sound-absorbing material for an automobile of claim 1, wherein the carbon nano-tube (CNT) is contained in a ratio from about 0.1% by weight to about 1.1% by weight based on the total weight of the polyol component and the isocyanate component, and wherein the sound-absorbing material comprises a semi-rigid foaming polyurethane foam having a density from about 18 kg/m³ to about 20 kg/m³.
 8. The sound-absorbing material for an automobile of claim 1, wherein the flame retardant filler is graphite.
 9. The sound-absorbing material for an automobile of claim 1, wherein the foaming urethane foam to which carbon nano-tubes are applied is sliced into sheets, and the sound-absorbing material further comprises a non-woven fabric press-molded on opposing surfaces of the sheets.
 10. A method of preparing a sound-absorbing material for an automobile, using foaming urethane foam to which carbon nano-tubes are applied, the method comprising: mixing about 70 to 90% by weight of high-molecular and low-molecular polyols with about 10 to 30% by weight of at least one additive comprising a foaming agent to prepare 100 parts by weight of a polyol component; preparing a mixed raw material by mixing about 120 to about 180 parts by weight of isocyanate, about 10 to about 20 parts by weight of a flame retardant filler, and about 0.1 to about 3 parts by weight of carbon nano-tubes with a stirrer for foaming thereinto, wherein parts by weight are based on 100 pats by weight of the polyol component; and adding the mixed raw material to the polyol component and mixing the resulting mixture under stirring to prepare a foaming undiluted solution; injecting the foaming undiluted solution into a mold to age the solution into a polyurethane foam which is foamed; and slicing the foaming polyurethane foam.
 11. The method of claim 10, wherein the foaming undiluted solution is prepared by stirring the mixture with the stirrer for foaming for about 20 to 60 seconds, adding the mixed raw material to the polyol component, and mixing the mixture under stirring at a high speed for about 5 to 20 seconds.
 12. The method of claim 10, further comprising: adhering a non-woven fabric on opposing surfaces of the sound-absorbing material to form a laminate; press-molding the laminate in a thermal molding machine, and then press-cooling the laminate in a cooling jig to prepare a semi-product; and trimming the semi-product into a desired design shape. 